1. Field of the Invention
The present invention relates to an exposing apparatus, and more particularly to an exposing apparatus using organic electroluminescent devices (hereinafter referred to as xe2x80x9corganic EL devicesxe2x80x9d) to expose a photosensitive material.
2. Description of the Related Art
Presently, array-type light sources for exposing a photosensitive material to record an image which employ light emitting diodes (LED), VF (Vacuum Fluorescent), organic EL devices, and the like, are being investigated.
An LED array has small errors in distances between LED devices within a chip, however, since the array is formed by jointing a plurality of chips, errors at joints in a direction in which the LED devices are arranged are large. That is, errors in distances between devices of different chips are large. Further, since wavelength and light intensity of LED devices largely depend on temperature, unevenness is likely to be caused and it is difficult to mount LED devices having different wavelengths on the same substrate. In addition, only LED arrays which emit red light have been presented.
A VF device includes a wire and a number of electrodes arranged so as to face the wire. However, the wire is slackened when it is long and, because of the limitation of the wire, it is difficult to make a long size VF, such as an A3 size VF. Further, hysteresis is likely to be caused by use of thermoelectrons. In addition, since either of the devices has a complex structure, it is difficult to arrange a number of devices in two dimension.
In contrast, organic EL devices, for which attempts for practical application have been remarkable in recent years, are excellent in the above-described points. However, organic EL devices have problems such as dispersion in properties such as light intensity, wavelength, light emission patterns between devices, change of light intensity over time, and the like, and are not sufficient for use for high quality images.
Correction techniques such as measurement of light intensity for each pixel and microscopic measurement of print density have been presented. However, the number of pixels to be corrected is several thousands for A3 width at 400 dpi (dots per inch), and it is still difficult to obtain sufficient image quality even when these pixels have been corrected.
In order to solve the above-described problems, an object of the present invention is to provide an exposing apparatus in which unevenness due to dispersion of properties among organic electroluminescent devices is prevented to form an optimal light emission pattern for exposure.
A first aspect of the present invention is an exposing apparatus including: a transparent substrate; and a plurality of rows of organic electroluminescent devices, each row including the organic electroluminescent devices disposed according to a predetermined spacing, the rows being disposed on a surface of the transparent substrate and displaced relative to each other, such that each organic electroluminescent device in one of the rows at least partially overlaps at least one organic electroluminescent device in another of the rows with respect to the direction of the rows.
There is slight dispersion in properties such as light intensity, wavelength, light emission form, and the like among the organic electroluminescent devices. Therefore, the organic electroluminescent devices are shifted relative to each other in the direction of arrangement so that at least portions of the respective organic electroluminescent devices are overlapped in the direction perpendicular to the direction of arrangement. Thereby, the dispersion of properties among the organic electroluminescent devices of different lines is cancelled and generally uniform properties can be obtained over the entire arrangements.
The position of each organic electroluminescent device in one of the rows may substantially correspond to the position of at least one organic electroluminescent device in another of the rows with respect to the direction of the rows, and a pixel may be formed using at least two of the organic electroluminescent devices.
The organic electroluminescent devices may include at least two types, each type arranged in rows according to the predetermined spacing, each row of the first type being offset by a predetermined amount with respect to the direction of the rows relative to each row of the second type so as to form a plurality of linear arrays of different organic electroluminescent device types on the transparent substrate, wherein the types of organic electroluminescent devices emit light in mutually different wavelength ranges, the transparent substrate consists essentially of a single substrate, and the arrays are shifted relative to each other such that each organic electroluminescent device in the array of one type of organic electroluminescent devices at most partially overlaps an organic electroluminescent device in the array of another type of organic electroluminescent devices with respect to the direction of the rows.
Further, the exposing apparatus may include a lens array including a plurality of lenses arranged opposing the rows so as to form lens rows, the positions of the lenses being shifted relative to each other from one lens row to another such that each lens in one of the lens rows at most partially overlaps a lens in another of the lens rows with respect to the direction of the rows, and the lenses being adapted for exposing a photosensitive material with light emitted from the organic electroluminescent devices.
In addition, the exposing apparatus may include an exposing drum, around which a photosensitive material is wound and exposed, wherein the transparent substrate is formed at the outside of the exposing drum with a cross section of the transparent substrate being formed in a circular arch shape whose center is at an axis of rotation of the exposing drum.
A second aspect of the present invention is an apparatus for exposing a photosensitive material, the apparatus including: a substrate; and a set of element rows formed by arranging a plurality of rows on the substrate in a direction substantially perpendicular to the rows, each row being formed by arranging a plurality of elements which emit light in the same wavelength range along the direction of the rows, the elements being spaced at first intervals, and the rows being displaced relative to each other with respect to the direction of the rows at second intervals which are smaller than the first intervals.